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Help with lawn mower magneto

Discussion in 'Off Topic Threads' started by joe kuhn, Jul 17, 2010.

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  1. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    I know, I should be shooting...

    I put the engine back together after discovering the main seal was blown - Sears 6.6 HP. Now there's no spark when holding the plug against the engine. No spark felt or seen. Green ground wire looks ok. Took the magneto off and removed the rust on all surfaces. Reinstalled and set the gap to the thickness of a business card. No spark. Magnet seems strong. Spark plug is new.

    Magneto module is $45. Looks like I try a replacment part. Anything else to check? I suppose I can rig up a ground wire of my own to be sure that's not the problem.

    Thanks,
    Joe
     
  2. halfmile

    halfmile Well-Known Member

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    If you have the safety handle there is a kill wire and a brake mechanism connected to it. usually a black wire.

    Tie the safety handle down while checking for spark.

    Ohm the coil. Make sure the spark plug connector is good, you can ohm it to ground. You can grab it when pulling the motor through just for fun.

    Good luck.

    HM
     
  3. trap906

    trap906 Member

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    disconnect the kill wire from the coil, make sure it's not touch ground, then spin the engine, if you then have spark the problem is a kill switch problem or the wire grounding out. I suppose we are talking about a electronic ignition, not a point type ? on techumseh engines, there are several different flywheel key configurations, some use an offset key, so make sure you have the right key, and that you don't have it installed upside down, causing flywheel to be offset in wrong dirrection, rust has no effect on the system, if a magnet works, it does or it don't. also, a electronic system usually requires the flywheel to spin about 200rpm range to fire. this requires a pretty good pull on the starter rope, you may not be able to get it to fire by just flipping flywheel with your hand. after these test, still no fire, replace the electronic unit,{coil}
     
  4. vdt

    vdt Active Member

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    check the air gap ,on the mag pick up try 10 thousands
     
  5. cubancigar2000

    cubancigar2000 Well-Known Member

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    some old motorcyle tricks coming back to ya Halfmile?
     
  6. WesleyB

    WesleyB Well-Known Member

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    Hey do those engines still have points under the flywheel? If not the ground are the points breaking contact to make the spark>?

    WesleyB
     
  7. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    I should pull the flywheel and take a look.

    I have an ohm meter, so will check it out tomorrow.
     
  8. halfmile

    halfmile Well-Known Member

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    Cuban, Lucas pickups had a habit of going bad. Lots of fun diagnosing them. They had a bakelite housing and a brush/spring setup for contact. The Bakelite would get leaky at the slightest imperfection. It was easier to diagnose at night, you could see the blue fire.

    Man, those English bikes packed a wallop.

    HM
     
  9. birddog1964

    birddog1964 TS Member

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    Set the air gap with a {brass} .10 thousandths blade, it should be the only brass one in a filler gauge set. The magnets on the flywheel will not stick to brass and it lets you get the proper gap. Also it does not have points under the flywheel. But make sure that you put the black wire back in the same place was it is a kill wire and some coils have a input terminal on them. I hope this helps.

    thanks
    lee
     
  10. Neil Winston

    Neil Winston Well-Known Member

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    Disconnect the kill button. Attach an ohmmeter to the loose wire and see that it is open when not operated, closed when it is.

    Attach the ground of a battery (6v is fine) to the mower frame. Disconnect the wire to the coil and brush it against the positive of the battery. With the plug touching the frame of the mower, see if there is a spark. Do not leave the battery connected through the coil long; it may be expecting lower voltage. Also, do not try this without a plug in the circuit as I described; the coil will arc internally and soon be not good even if it was when you started.

    If there is no spark, it's new coil time.

    If there is, the coil is probably OK. Then you have to see

    1. if there is power to the points, that is, if the magnets are OK (will it pull a screwdriver pretty hard?)

    2. If the points are getting power (is the wire to it patent?)

    3. Do the points open and close electrically as well as mechanically? Your ohmmeter will check this too. When the points are closed, expect a resistance near zero. When open, near infinity. And the break should be "clean," that is,it should take very little flywheel movement to go from (say) 0.2 ohms to infinite. An analogue meter is preferred over a digital one for this test. In fact, an analogue meter is best for all these tests.

    Good luck; you should have either spark or a clear path to spark in under five minutes.

    Neil
     
  11. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    This is a push mower; no battery, no points, etc. Just a magneto which I checked and I get nothing - no clear path - between the wire that attaches to the spark plug and the magneto (the stationary concave part that the flywheel magnet passes by. This is part 100 in the following website:

    http://beta.searspartsdirect.com/partsdirect/getSubComp.pd?modelNumber=143976600&productCategoryId=1503500&brandId=0247&brandDescription=CRAFTSMAN&modelName=ENGINE&diagramPageId=00001&componentDescription=ENGINE%20143.976600&documentId=10045231&blt=06&prst=0&shdMod=143.976600

    There is no kill button. There is a brake, but it's under the flywheel, so I don't know how it works yet. There is a part called an 'element', part #6, I wonder how it might figure into my problem.

    Time to yank the flywheel...
     
  12. deuce

    deuce Member

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    Joe,

    If I understand your last post correctly, you are checking for continuity between the plug wire and the magnet. You will not get a reading this way because the plug wire connects to the coil. To check the plug wire, pierce the coil covering with a pin or small nail and use it as a terminal to check the wire.

    Jim
     
  13. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    Thanks Jim. Was wondering about that black box. I wish I could find a decent picture of the 'module' as they call it. Coil must be inside the black box. I think I'm going to get a new module because the spark plug wire is a part of it all, like you say. I can't get continuity with the ground wire attachment and anything else on either end of the 'module' including two leads above the ground. (New coil behaves the same. Still don't know how to test this coil; maybe the only way is to replace it and see if it works.)

    There's a brake underneath the flywheel, but no kill switch to be malfunctioning that I can see.

    Part is in stock...
     
  14. halfmile

    halfmile Well-Known Member

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    The brake also kills the engine via a black wire, grounding the magneto.

    At least in all the examples I know. It's a vital safety feature.

    Older mowers without the brake had a black wire that grounded when the throttle went totally off. This was usually by the carb.

    HM
     
  15. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    Thanks HM. Didn't get the flywheel off cuz I don't have a puller. New coil did the trick. What fails on coils?

    Got some feeler guages. Used the one marked '.010' - for ten thousandths.

    Runs like a top now. Started first pull. Will change the oil after the first mowing.

    Ye haw. Thanks everybody.

    Joe
     
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